Techniques for depositing substances, such as layers of semiconductor material, using a plasma that is formed into a jet, are well known. For example, my U.S. Pat. Nos. 4,471,003 and 4,487,162 discloses arc jet plasma deposition equipment which utilizes a plasma for deposition of semiconductors and other materials. Ions and electrons are obtained by injecting an appropriate compound, such as a silicon compound, into an arc region, and a jet (or beam) is formed by utilizing magnetic fields to accelerate and focus the plasma. Recently, equipment of this type has been used to deposit synthetic diamond. Superior physical and chemical properties make diamond desirable for many mechanical, thermal, optical and electronic applications, and the ability to deposit synthetic diamond by plasma jet deposition holds great promise, particularly if plasma jet techniques can be improved for this and other purposes.
When a heated plasma jet impinges on a substrate, a significant fraction of the plasma beam is channeled around the substrate without coming in contact with the substrate surface. The energy invested in processing the bypassing portion of the flow into the necessary species of the plasma (e.g. carbon molecules, radicals, and atomic hydrogen, for the case of diamond deposition) does not result in effective deposition, and this substantially increases the cost of the process. Inefficient deposition also increases the time necessary to obtain a desired layer thickness and can waste constituent feedstock. Recycling of feedstock (particularly hydrogen) is possible, but also involves some cost.
It is among the objects of the present invention to improve the efficiency of plasma jet deposition of substances.